With an increase in the density of LSI, the circuit line width of semiconductor devices has decreased through the years. To form a desired circuit pattern of semiconductor devices on a wafer, an original image pattern (i.e., a mask or, particularly, a reticle for use in steppers or scanners) with high precision formed on a quartz mask blank is transferred onto a wafer with its size reduced by using reduction projection light-exposure apparatus. The original image pattern with high precision is written by an electron beam writing apparatus, i.e., with a so-called electron beam lithography technique.
Examples of the electron beam writing apparatus include a multi-beam writing apparatus with an increased throughput by applying a large number of beams at a time with a multi-beam technique. In this multi-beam writing apparatus, for example, multiple beams are formed by letting an electron beam emitted from an electron gun pass through an aperture member having a plurality of apertures, and blanking control is performed for each of the beams by a blanking aperture array. Unblocked beams are diminished in an optical system and applied onto a desired location on a mask blank to be written.
The blanking aperture array includes a substrate in which multiple holes are formed, blankers formed around the respective holes, and a control circuit that applies a voltage to the blankers. Normally, after MOS field-effect transistors (MOSFET) constituting the control circuit are formed, a passivation film (protection film) made of, for example, a silicon nitride film is formed on the surface of the substrate. Thus, an insulator film such as a silicon nitride film is exposed on the surface of the blanking aperture array. When the blanking aperture array is irradiated with an electron beam and/or electrons scattered by an aperture, the surface of the blanking aperture array is electrically charged. This may cause the following problems. The gate insulator of the MOSFET may be subjected to an electrostatic breakdown, failing to perform blanking control. The courses of beams that pass through the holes may be deflected by the electric field, causing deviation of trajectory (irradiation positions on a blank) or defocus, thereby reducing drawing accuracy.